Diamond has many extraordinary properties, including superlative hardness, thermal conductivity, and optical transmissivity. Synthetic diamond produced by chemical vapor deposition has become commercially viable for practical applications such as wear parts, heat sinks, and optical windows. However, while the cost of producing CVD diamond has decreased in recent years, it is still quite expensive, especially high quality CVD diamond.
There are several components that contribute to the relatively high cost of producing synthetic diamond by chemical vapor deposition. One such cost component is the investment in the capital equipment itself. A second cost component is the cost of reagents. For the most common processes (e.g. arc jet plasma CVD, microwave plasma CVD, and hot filament CVD), which use hydrogen-assisted deposition, hydrogen gas and a hydrocarbon gas are the feedstock gases for the deposition process, and the ratio of hydrogen to hydrocarbon is of the order of 100 to 1. In some processes, hydrogen is consumed in relatively large quantities, so the cost of the hydrogen gas can be a very significant component of the cost of producing CVD synthetic diamond. Another very significant cost component of these processes is the electric power cost of dissociating the hydrogen gas (H.sub.2) into the atomic hydrogen that is used at the deposition region to assist diamond growth. This cost component can be considered as the product of two related sub-components; namely, the efficiency with which the electric power dissociates the hydrogen, and the efficiency with which the dissociated hydrogen is brought to the deposition surface. The product of these two efficiencies determines the efficiency with which electric power is converted to dissociated hydrogen that is made available at the location at which it is useful in assisting the diamond deposition process.
Existing diamond deposition techniques tend to be inefficient in their use of hydrogen and/or their use of electric power to obtain dissociated hydrogen at the deposition surface. Arc jet plasma techniques have relatively high fixed costs, produce wasteful heating, and transport and use atomic hydrogen convectively and with relatively poor efficiency. Microwave and planar hot filament CVD systems can both create atomic hydrogen over a relatively large, distributed area. High temperature electrons in microwave plasmas efficiently dissociate hydrogen gas with minimal gas heating, but microwave systems employ costly power supplies, raising fixed costs, and they have poor transport efficiency. Planar hot filaments use inexpensive D.C. power, and transport efficiency is high when the filaments are brought close to the deposition surface. However, hot filament systems have very low values of dissociation efficiency, wasting most of the input energy on sensible gas heating.
It is among the objects of the present invention to provide a technique and apparatus for producing synthetic diamond film with increased efficiency and at lower cost.